The present invention relates to a vehicle occupant protection system, and in particular to a vehicle occupant protection system which can reduce a deceleration acting upon a vehicle occupant at the time of a vehicle crash.
In recent years, various proposals have been made in regard to automotive vehicle body structures to maximize the protection of vehicle occupants at the time of a vehicle crash. For instance, proposals have been made to minimize the deceleration of the part of the vehicle body occupied by vehicle occupants by properly selecting the deformation of the remaining part of the vehicle body, and preventing the former part of the vehicle body from deforming (see Japanese patent laid open publication No. 7-101354, for instance).
However, it may be difficult to reduce the deceleration of the vehicle occupant in the case of small cars which do not provide adequate deformation strokes of the parts of the vehicle body other than the part occupied by the vehicle occupant only with such conventional approaches which essentially consist of attempts to reduce the deceleration of the passenger compartment by controlling the deformation mode of the vehicle body.
Further, it is generally impossible to integrally attach a vehicle occupant to a vehicle body even if the seat is fixedly attached to the vehicle body because the seat belt for restraining the vehicle occupant to the seat has an inevitable slack. Thus, when a vehicle crash occurs, the forward inertial force acting upon the vehicle occupant at the time of a vehicle crash starts rising only after the vehicle occupant is fully restrained by the seat belt. Further, because the seat belt inevitably has a certain resiliency, the deceleration acting on the vehicle occupant, who tends to continue to move forward, reaches a maximum level when the maximum elongation of the seat belt takes place. The maximum deceleration level increases as the forward movement of the vehicle occupant with respect to the vehicle body under the inertial force increases, and is known to substantially exceed the average deceleration of the vehicle body. Therefore, in order to minimize the impact which the vehicle occupant receives at the time of a vehicle crash, it is necessary to minimize the time delay in the rise in the deceleration of the vehicle occupant with respect to the deceleration of the vehicle body and thereby reduce the forward movement of the vehicle occupant with respect to the vehicle body.
Proposals have been made in copending US patent application Ser. Nos. 09/377,366 and 09/376,888 both filed on Aug. 18, 1999, to impart a relative deceleration and acceleration to the vehicle seat or the member carrying the vehicle seat with respect to the main part of the vehicle body so that the vehicle occupant may experience a deceleration from an early stage of a vehicle crash, and the maximum vehicle occupant deceleration may be reduced by distributing the inertia force acting on the vehicle occupant over a longer period of time. The contents of these applications are hereby incorporated in this application by reference.
In view of such problems of the prior art and the recognition by the inventors, a primary object of the present invention is to provide a vehicle occupant protection system which allows the peak deceleration acting upon a vehicle occupant at the time of a vehicle crash to be minimized for a given deformation stroke of the vehicle body.
A second object of the present invention is to provide a vehicle occupant protection system which allows the deceleration acting upon the vehicle occupant at the time of a vehicle crash to be spread over time so as to minimize the peak deceleration acting upon the vehicle occupant.
A third object of the present invention is to provide a vehicle occupant protection system which allows the peak deceleration acting upon the vehicle occupant to be minimized even though the size of the vehicle body is limited.
A fourth object of the present invention is to provide a vehicle occupant protection system which is simple in structure, and light in weight.
A fifth object of the present invention is to provide a vehicle occupant protection system which can be adjusted easily to achieve a preferable deceleration pattern of the seat for minimizing the peak deceleration of the vehicle occupant.
According to the present invention, these and other objects can be accomplished by providing a vehicle occupant protection system, comprising: a seat (8) which is fitted with a seat belt (9) for restraining a vehicle occupant in the seat; a first member (2) attached to the seat and supported on a vehicle body so as to be movable in a direction of an input crash load resulting from a vehicle crash, the first member being adapted to deform under the crash load while supporting an inertial force of said seat upon occurrence of the vehicle crash; a second member (1) which is connected to a main part of the vehicle body and adapted to deform under the crash load while supporting an inertial force of the vehicle body; and a power actuator (10) for applying a forward force to said first member relative to said second member with a certain time delay after the occurrence of the vehicle crash, the first member being adapted to substantially deform only after said forward force is applied to said first member by said power actuator upon occurrence of the vehicle crash.
Because the second member deforms upon the occurrence of a vehicle crash while the first member resists deformation during an initial phase of the crash, the restraining capability of the seat belt is enhanced by applying to the seat a deceleration higher than the vehicle body deceleration during the initial phase of the vehicle crash. Thereafter, a forward force (and thus, opposite in direction to the crash load) is applied to the seat so that the forward inertial force acting on the vehicle occupant is canceled, and the equalization of the decelerations of the vehicle body and the vehicle occupant is achieved in an early stage of the crash.
In one embodiment, the power actuator preferably comprises a cylinder (11), a piston (2a) received in said cylinder to define an enclosed chamber in cooperation with said cylinder, and a propellant (12) which is received in said chamber and adapted to produce a high pressure gas upon ignition. In this way, by igniting the propellant to apply a forward force to the first member which is connected to the seat at an appropriate timing, a desirable time history of the deceleration of the seat for minimizing the peak deceleration of the vehicle occupant restrained in the seat can be achieved.
Preferably, a stopper (2c, 11a) is provided between said first and second members for joining said two members integral to each other following a prescribed rearward displacement of said first member relative to said second member upon occurrence of the vehicle crash, and said power actuator is provided with a vent valve (2d, 11b) for expelling said high pressure gas from said chamber when said first member has been joined with said second member by said stopper. In this way, after application of the forward force to the first member by the high pressure gas, an integral deceleration of the first and second members can be preferably achieved without being affected by the high pressure gas in the chamber of the cylinder.
In view of simplifying the system configuration and manufacturing process, it may be preferable if said stopper is provided between a part (2c) of said piston and an end (11a) of said cylinder, and said vent valve is formed between a part of said piston and said cylinder.
Further, the system preferably comprises a detector (14) for detecting a prescribed rearward displacement of said first member relative to said second member upon occurrence of the vehicle crash, and an igniter (13) for igniting said propellant according to a signal from said detector. The detector may consist of a limit switch (14) or a pressure sensor for detecting a pressure increase inside said cylinder resulting from said prescribed rearward displacement of said first member relative to said second member upon occurrence of the vehicle crash.